I purchased a S & W 625 that has a SDM fiber optic tube front sight. The plastic tube is missing and I ordered one on e-bay. The sights that have holes all the way through call to heat up both ends of the tube, the SDM sight has one end that is drilled all the way through but the other end is a blind hole. Do you heat up only one end and pull it into the sight, or is the blind hole end glued in to hold the tube in ?